1. Field of the Invention
The invention relates to a projection type display apparatus, and more particularly to a projection type display apparatus which uses a display device having a fixed number of display pixels, such as a liquid crystal panel as a light valve.
2. Description of the Related Art
As a projection type display apparatus which uses a display device such as a liquid crystal panel, there is known, for example, a rear projection type display apparatus (hereinafter called a rear projector). The rear projector is adapted to display an image which is projected onto the rear surface of a screen from the projector so that a viewer can view the image from the front of the screen.
The rear projector using the liquid crystal panel will be described as follows: A configuration of the rear projector has the liquid crystal panel which is irradiated with light emitted from a light source; a driver circuit which drives this liquid crystal panel by an image signal; and a projection lens for projecting the light emitted from the liquid crystal panel onto a screen, whereby the image light from the projection lens is projected on to the rear side of the screen. It is to be noted that the image light from the projection lens is reflected by a mirror to be projected onto the screen. Furthermore, an incoming image signal for driving the liquid crystal panel is supplied from a signal processing circuit, which is controlled by a control circuit, such as a microcomputer.
Where the liquid crystal panel is of a transmission type, the light projected from the light source is made incident upon one face of the liquid crystal panel and goes through it, so that the resultant outgoing light is subject to intensity modulation by means of the image signal and made incident upon the projection lens. The light from the projection lens is diverged and reflected by the mirror and projected onto the rear face of the screen. As a result, an image displayed on a display face of the liquid crystal panel is projected as scaled up onto the screen visually. In such a manner, a viewer can view the scaled up image on the screen.
One of such rear projectors is disclosed in, for example, Japanese Patent Publication No. 2569632.
In the case where the liquid crystal panel has 1920×1080 display pixels to represent an image signal (1080p) which accommodates an image having the same number of pixels, the image is displayed using an overall display surface of the screen. If, however, an image (720p) having a smaller number, for example 1280×720, of pixels than those given above is to be displayed, the image is displayed in an area having as many as its number of pixels and, therefore, it is rendered smaller on the screen. That is, the smaller the number of pixels, the smaller the relevant image displayed on the screen.
Thus, in the case of the conventional projection type display apparatus, if the number of pixels contained in the incoming image signal is smaller than the number of all of the display pixels of a display device (for example, liquid crystal panel), the image is displayed correspondingly smaller on the screen and so may be degraded in impact etc., so that a viewer may feel uncomfortable.
Therefore, to cope with such a situation, such an approach is employed that if an image having a small number of pixels is input, signal processing is performed to convert the number of pixels contained in the relevant image signal so that this number may agree with the number of all the display pixels of the display device, for example, the liquid crystal panel, in order to display the converted image on the liquid crystal panel, thus displaying it as scaled up on the screen.
Such an approach for increasing or decreasing the number of pixels contained in the image signal by signal processing is herein called scaling. By this scaling processing, which is performed utilizing a microcomputer, the number, type, etc., of pixels are detected on the basis of the input image signal, to perform scaling in such a manner as to match the number of pixels of a display device employed. As a result, an image display method for the liquid crystal panel is switched, thus eliminating the disadvantage that the display viewing surface is reduced in size on the screen.
Display by scaling, however, may fundamentally lead to impairment of the feeling of focus because some pixels which are not actually present are produced by operational processing, such as interpolation. To increase the size of the display viewing surface in an integer multiple, for example, such processing can be performed as to scale up in that multiple the signal containing all of the pixels of a relevant image. Actually, however, a scaling factor of 1.5, etc., is required. To scale up the image by a factor of 1.5, etc., requires complicated interpolation and the image signal obtained as a result of interpolation is distorted more or less, thus making it impossible to provide optimal screen display.
Thus, the expansion of the display viewing surface by scaling has the disadvantage that a signal processing circuit becomes complicated thereby increasing the cost and requiring prolonged time for development.